Enzymatic dehalogenation of gas phase substrates with haloalkane dehalogenase

Haloalkane dehalogenase is an enzyme capable of catalyzing the conversion o f short-chained (C-2-C-8) aliphatic halogenated hydrocarbons to a correspon ding primary alcohol. Because of its broad substrate specificity for mono-, di-, and trisubstituted halogenated hydrocarbons and cofactor independence , haloalkane dehalogenases are attractive biocatalysts for gas-phase biorem ediation of pollutant halogenated vapor emissions. A solid preparation of h aloalkane dehalogenase from Rhodococcus rhodochrous was used to catalyze th e dehalogenation reaction of 1-chlorobutane or 1,3-dichloropropane delivere d in the gas phase. For optimal gas-phase dehalogenase activity, a relative humidity of 100%, a(w) = 1, was desired. With a 50% reduction in the vapor -phase hydration level, an 80% decrease in enzymatic activity was observed. The enzyme kinetics for the gas-phase substrates obeyed an Arrhenius-"like " behavior and the solid haloalkane dehalogenase preparation was more therm ally stable than its water-soluble equivalent. Triethylamine was added to t he gaseous reaction environment in efforts to increase the rate of reaction . A tenfold increase in the dehalogenase activity for the vapor-phase subst rates was observed with the addition of triethylamine. Triethylamine altere d the electrostatic environment of haloalkane dehalogenase via a basic shif t in local pH, thereby minimizing the effect of the pH-reducing reaction pr oduct on enzyme activity. Both organic phase and solid-state buffers were u sed to confirm the activating role of the altered ionization state. (C) 200 0 John Wiley & Sons, Inc.